Nick Gibb, the schools minister, is to marry his long-term partner after deciding to tell his family that he is gay.

Gibb, 54, and Michael Simmonds, the chief executive of the Populus polling organisation, who have been together for 29 years, are to marry later this year. The couple kept their relationship secret until Gibb informed his family last week.

Gibb arranged for his brother to inform his 79-year-old mother. “I wanted to give her a chance to process the information so she didn’t say something she might regret,” he told the Times.

Gibb had dinner with his mother on the night before the Queen’s speech last week and raised his personal life with her over coffee.

“I think my mother was initially shocked – that’s an age thing – but then very supportive and what she wants is for me to be happy,” he said. “We are close, so to her being a loving family is more important than anything else.”

Gibb said that the couple had felt comfortable about keeping their relationship secret because they met and fell in love in what he described as a different era in the mid 1980s.

“We met in a different era so you are in a way locked into that and we were comfortable with it,” he said. “We have a wonderful life together. We are both very private people.”

He says he can remember the exact time and place they met – an Adam Smith Institute Next Generation dinner when he was 26. “We realised very quickly we had an interest in common and it was pretty rapid. We fell in love very quickly.

“It was harder then. [Homosexuality] was only made legal in 1967. There was discrimination in industry and the professions.

“It was easier to have a relationship that wasn’t known about. It didn’t really bother us, we both had successful careers. We just got on with life.

“It’s not a matter of being liberated because I’ve never felt unliberated. Michael and I are both very strong characters, we were never going to let societal attitudes affect our happiness and our way of life.”

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Gibb, who said the couple kept separate houses for years even when they were living together and who have not attended family events such as Christmas together, said they had decided to get married in part because they are worried about practical considerations.

“If one of us was ill and had to go to hospital it would be awful if we couldn’t be there for each other,” he said.

A deep belief in equality prompted them to spurn the chance to take out a civil partnership. They were always determined to wait until the law changed to allow them to marry.

Gibb, who praised David Cameron for introducing equal marriage, said: “Marriage has only been possible recently. We were never in favour of civil partnerships because we felt there should be the same approach for us and other couples. We both felt strongly we would wait until marriage became legal.”

Gibb said he would work hard to ensure that the word gay is not used as a pejorative term by children.